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From Toke Eskildsen ...@statsbiblioteket.dk>
Subject Re: In-memory docValues speedup
Date Wed, 22 Jun 2016 11:34:42 GMT
Joel Bernstein <joelsolr@gmail.com> wrote:
> I've tested with the Direct docValuesFormat which is uncompressed
> in-memory. But I haven't seen any noticeable performance gain. I've been
> meaning to dig into exactly why I wasn't seeing a performance gain, but
> haven't had the chance to do this yet.

If this is about Direct PackedInts (1 entry in an underlying array = 1 value) vs. Packed PackedInts
(bits must be shifted and masked out from the underlying array), then there is little time
difference when retrieving values. I think this is caused by memory access being slow and
computation being fast.

It was discussed in Solr-4096. There is still some old and very poorly labeled charts at http://ekot.dk/misc/packedints/


Thinking out loud, I seem to remember some talk about the current PackedInts-using docValues
code being hard for the JVM to inline? Could the problem be the number of indirections for
a lookup, rather than the underlying data structure?

- Toke Eskildsen

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